Visuals (listed by section)

Figure 7-1. Prometheus

In Greek mythology, Prometheus is credited with bringing fire to humankind from the gods. As the earliest example of humans harnessing chemical energy, fireâ€™s importance to the development of human culture cannot be overstated. The light from fire allowed humans to remain active after dark, and it provided protection from predators and insects. Cooking also makes food more digestible, allowing the body to extract more energy from it. (Unit 7, Section 1)

Figure 7-2. Pumped-Storage Hydropower

Pumping water to a storage pool above a power plant when electricity demand is low increases its potential energy, which can be used to generate electricity later by releasing the water and letting it flow down through turbines. (Unit 7, Section 2)

Figure 7-3. Heating Curve for Water

In this heating curve, water starts out in the solid phase (ice) at -20°C. As the water is heated, its temperature rises. Once it reaches the melting point, continued heating no longer increases the temperature. Over the length of the melting plateau, the additional heat goes into breaking molecules free from their crystal structure. Only when melting is complete will the temperature rise again. (Unit 7, Section 2)

Figure 7-4. Comparing Thermal Energy

Imagine that two flasks of equal size are left on a table, one holding a liter of water and the other holding two liters of water. Once the water has reached room temperature, the water will be the same temperature in the two flasks. But the larger quantity of water will have more thermal energy than the smaller quantity, because two liters of water contain more particles than one liter. Twice as much ice would have to be added to the beaker on the left to cool down the water to the same temperature as the beaker on the right. (Unit 7, Section 3)

Figure 7-6. Four-Stroke Cycle in a Gasoline Engine

In a four-stroke internal combustion engine, pistons move up and down, pulling fuel into combustion chambers, where it is compressed and ignited. Fuel ignition causes gases to expand, pushing the pistons down and transmitting power that moves the car. (Unit 7, Section 4)

Figure 7-10. Coffee Cup Calorimeter

When a chemical reaction occurs in the coffee cup, the heat generated by the reaction will be absorbed by the water in the cup. Because Styrofoam is a good insulator, nearly all the thermal energy from the reaction will stay in the cup and not be lost to the surroundings during the experiment. (Unit 7, Section 7)

Figure 7-12. Magnesium Ribbon Burning

A strip of magnesium burning. Because the reaction produces intense light, magnesium was the main component of photographic flash powder in the late 1800s. Today, many fireworks contain magnesium because it produces such brilliant white light. (Unit 7, Section 8)

Sidebar Image. Explosive Energy

High explosives, like the one used in the demolition shown above, release tremendous amounts of enthalpy very quickly due to the formation of high-enthalpy bonds. This in turn heats the air and the reactants which then rapidly expand causing destruction. (Unit 7, Section 9)